1. Field of the Invention
The present invention relates to a shredder for cutting rejected wallboard into particles of selected size and shape compacted for disposal or suitable for recycling into wallboard.
Wallboard usually consists of a core of gypsum sandwiched between two layers of paper. It conventionally measures 1/201" thick, 48" wide and 8 to 20 feet in length. In manufacture, a plaster slurry containing a catalyst is mixed and discharged on a moving web of paper. The edges of the bottom paper are scored and folded so that the slurry is completely contained between that sheet and the top paper, which is laid on the slurry. The paper surfaces provide strength and paintability to the finished board and form a continuous mold within which the gypsum is cast. Within about five minutes after forming, the gypsum is sufficiently hard to be cut, after which the sheets are dried further before storage and shipment.
A wallboard machine operates continuously and most rejects occur at start-up and during splicing of the paper. During start-up, the upper and lower papers are typically folded into a nose cone and the paper started through the machine. At this time, water containing varying amounts of gypsum and catalyst is directed onto the first 50 to 60 feet of paper passing through the machine before the mix is correct. The rejected material during this interval consists of dry paper, wet paper and paper containing cured and uncured slurry of variable composition. When the paper is spliced and during normal runs, the rejected material primarily consists of torn wallboard or wallboard which is imperfectly wrapped or sized.
Rejected wallboard can be either recycled or dumped. When it is dumped, the boards are typically dropped into a trash gondola but their size and shape do not allow for close packing, resulting in the gondola filling up long before its weight capacity is reached. If the wallboard could be shredded into regularly sized, relatively small particles, this would increase the density of the material dumped into the gondola and fewer containers would be needed, resulting in significant savings in hauling costs. Some wallboard plants can recycle rejected wallboard if it is cut to a correct size. For example, when the gypsum rock is pulverized in a roller mill, shredded wallboard can be added with the rock as long as the particles are no bigger than about 2.times.2". It is very difficult, however, to control particle size of the wallboard in a conventional shredder using a grate or screen since the combination of uncured gypsum mix and paper produces a sticky mass which tends to block the discharge holes. If the grate or screen is removed, on the other hand, there is no control on the size of the product, especially the paper, and it then tends to gum up the roller mill or, if the material is being dumped, adversely effects density, increasing disposal costs.
2. Brief Description of the Prior Art
Shredders having a scissoring action making use of intermeshing comb cutters on the rotor and stationary cutter have been used in the past. These mills, however, do not provide a "punch and die" action in the sense that the material is not cleanly sheared because it is impracticable to machine the comb cutters to mesh in such close tolerance that the material undergoing reduction is both (1) supported by the projecting teeth of the stationary comb at the cut made by the rear of the cutter pockets in the opposing comb and (2) supported by the stationary comb adjacent the rear of the cutter pockets in said comb at the cut made by the projecting teeth in the opposing comb. Usually, some gap is provided between the rear of the cutter pockets and the corresponding projecting teeth of each set of opposing combs. While this arrangement is all right for friable materials, it is not well suited for nonfriable materials such as wallboard which requires far more shearing force.
In view of the above, it is an object of the present invention to provide a shredder with an improved comb cutter providing "punch and die" shearing action suitable for shredding wallboard into particles of selected size and shape. It is a further object to provide means for metering the incoming feed into the shredder. Other objects and features of the invention will be in part apparent and in part pointed out hereinafter, the scope of the invention being indicated by the subjoined claims.